One thousand three hundred and eighty-two patients with rheumatoid arthritis requiring second-line therapy at 108 centres were entered into an open 6-months prospective tolerability study of enteric-coated sulphasalazine 2 g/day (Salazopyrin EN-tabs). Clinical and laboratory variables were measured, any adverse reactions and the reasons for withdrawal of medication were recorded. The outcome of therapy was known in 87.5% of patients entered of whom 65% continued with sulphasalazine beyond the 6-month study period. 3.2% withdrew for reasons unrelated to treatment, 5% for lack of effect and 26.8% due to an adverse event; gastrointestinal/central nervous 66.6%, rash 15.4%, haematological 5.1%, hepatic 4.7% and miscellaneous 8.1%. 1.2% of patients experienced potentially serious reactions: anaphylactic, haematological and hepatic. The majority of adverse events occurred early and were reversible upon cessation of medication. No clear relationship between withdrawal due to an adverse event attributed to sulphasalazine and the nature of the concomitant non-steroidal anti-inflammatory drug was identified.